An ion trap is an apparatus used to confine or isolate a charged particle, such as an electron. One such apparatus is known as a Penning trap. A Penning trap uses a magnetic field and an electrostatic field together to trap a charged particle. The magnetic field causes the charged particle to perform a rotational movement with the direction of the magnetic field being the axis of the rotation. This effectively confines the charged particle to a plane normal to the direction of the magnetic field. The electrostatic field is arranged to confine the charged particle at a location along the direction of the magnetic field, by providing a potential well for the particle at the desired location.
In order for a Penning trap to confine a charged particle effectively and to be useful for performing measurements on the trapped particle, it is important both for the magnetic field to be homogeneous and for the electrostatic field to be harmonic at the location the charged particle is to be trapped. This places constraints in the design of a conventional Penning trap and its variants, generally making them complex and expensive.